Conventionally the active pulser ring system and the passive pulser ring system are adopted to detect rotating speeds of wheels.
FIG. 1 shows one example of the active pulser ring system which has a magnet pulser ring M with alternative N and S poles and a magnetic sensor H having e.g. Hall elements to generate wave forms a) and b). The rotations of the pulser ring are detected by the magnetic sensor H through changes of the poles. This system is characterized by the pulser ring which generates magnetic forces.
FIG. 2 shows an example of the passive pulser ring system which has a rotating pulser ring S with alternative strong and weak magnetic resistances and an outside magnet means M. The magnetic forces from outside is detected by a magnetic sensor C through the alternative strong and weak magnetic resistances to measure rotational speed of the pulser ring S. This system is characterized by the pulser ring which receives the magnetic forces from outside, which is disclosed e.g. in Japanese Utility Model First Publication No. 60-112757, U.S. Pat. Nos. 4,161,120 and 5,002,287.
Compact systems to detect rotations of the bearing are developed to have a pulser ring installed between the outer and inner rings of the bearing as disclosed in U.S. Pat. No. 4,688,951, European Patent Publication No. 0,375,019 and United Kingdom Patent Publication No. 1,640,861.
The pulser ring is integrally incorporated in the seal structure radially between the inner and outer rings of the bearing to make compact the whole rotation detecting device.
Active pulser rings integrally provided within a seal means between the outer and inner rings of the bearing are disclosed in European Publication NO. 0,378,939, French Patent Publication No. 2574501, Japanese First Patent Publication No. 62-242130.
However, it is still required to prevent the installed magnet from being adversely affected by an outside magnetic field when the bearing is assembled with the installed magnet, and for improving the mechanical strength of the magnet so as not to damage the magnet upon assembling the bearing.
For example, ferrite magnetic plates with relatively lower mechanical strength as shown in European Patent Publication No. 0375019, and in Japanese Patent Publication No. 62-242130 must be cared on cracks and deformation etc. upon press-fitting into a seal groove in the outer ring. Generally, such magnetic plates are bonded to a steel plate frame as disclosed in French Patent Publication No. 2,574,501.
It is still, however, required to prevent the magnet from being adversely affected by the outside magnetic field even in the case where the magnet is bonded to the steel plate frame.
On the other hand, the passive pulser ring integrally provided within a seal structure between the outer and inner rings of the bearing is disclosed in U.S. Pat. No. 4,850,722, Japanese Patent publication No. 62-242130 and Japanese Patent Publication No. 64-21219.
In this type of bearings having such a passive pulser ring, appreciable differences of the magnetic resistances and precise measuring gaps with reference to the magnetic sensor are required.
Japanese Utility Model First Publication No. 60-112757 discloses a bearing structure where a passive pulser ring is mounted onto a seal frame, not onto the outer peripheral surface of the housing, with notches provided along its periphery and radially projecting therefrom so as to detect magnetic resistances in the axial direction of the housing. This type of bearing structure is difficult to be made compact because of axially extending teeth-section.